1. Field of the Invention
The present invention relates to an organometallic complex usable as a hydrogen storage material or the like and a method for producing the same.
2. Description of the Related Art
As is known in the art, fuel cells generate electricity using a fuel gas such as hydrogen gas supplied to an anode and an oxidant gas such as oxygen gas supplied to a cathode. Therefore, for example, a fuel-cell car containing the fuel cell is equipped with a gas storage vessel for storing the hydrogen gas. The fuel-cell car is driven by utilizing the air as an oxygen-containing gas and the hydrogen gas supplied from the vessel as reactant gases.
As is clear from the above, as the gas storage vessel has a higher hydrogen storage capacity, the fuel-cell car can be driven over a longer distance. However, when the fuel-cell car is equipped with an excessively large gas storage vessel, the fuel-cell car has an increased weight, resulting in a high load on the fuel cell disadvantageously. From this viewpoint, various studies have been made on a gas storage vessel having a high hydrogen storage capacity with a small volume.
In one attempt, a material for storing or adsorbing hydrogen (hereinafter referred to as a hydrogen storage material) such as a hydrogen storage alloy is placed inside the gas storage vessel. The hydrogen storage material is capable of incorporating hydrogen into its molecular structure, so that a larger amount of hydrogen can be stored in the vessel as compared with the vessel volume.
An organometallic complex is known as a preferred hydrogen storage material. The organometallic complex is a compound containing a metal core and an organic group bonded thereto.
In the organometallic complex, the organic group is bonded to the metal core in a regular manner. Therefore, pores having relatively uniform diameters may be formed in its molecular structure. An inner wall of each pore may act as a site for physically adsorbing hydrogen. Of course, it is preferred that the complex has a higher hydrogen storage capacity.
B. Panella, M. Hirscher, H. Putter, and U. Muller have reported hydrogen adsorption properties of [Cu3(benzene-1,3,5-tricarboxylate)2(H2O)3]n (hereinafter referred to as the Cu-BTC) at various temperatures in Advanced Functional Materials, 16(4), 520-524 (March 2006), “Hydrogen Adsorption in Metal-Organic Frameworks: Cu-MOFs and Zn-MOFs Compared”. According to this report, the hydrogen adsorption amount of the complex is 3.6% by weight at 77 K (pressure extrapolation value), and is 0.35% at the room temperature 298 K under a hydrogen pressure of 65 bar (6.5 MPa). Thus, the hydrogen adsorption amount is less than 0.4% by weight at the room temperature.
However, the fuel-cell car is generally driven at an environmental temperature around the room temperature, so that it is preferred that the hydrogen storage material of the organometallic complex exhibits a larger hydrogen adsorption/release amount around the room temperature.